Many different kinds of rotary engines and compressors are known. It has long been the goal to replace reciprocating compressors and engines with rotary machines, however certainly in the case of engines, very few have become successful and widely used today.
In the field of rotary engines, the design which has had most development and use is the well-known Wankel engine. However this suffers from a number of problems, one of which is wear issues with the internal rotor seals, and another is that it is not a true rotary machine, in that there are still eccentrically moving parts which generally requires there to be two counterbalanced rotors, or use made of rotating counterweights. Furthermore, the location of the tip seals on the inner rotor means that these cannot be replaced without stripping the entire engine down.
It is possible to use a Wankel design and to spin both the inner rotor and the outer casing axially, thus having no eccentric components, as in the very first version, the DKM engine. However with this design the sealing points are on the inner rotor, which means that the sliding surface containing the inlet and exhaust ports must be in the shell or casing. This means that the ports and ducts which the sealing points sweep past to control the fluid transfer must be located in the shell. It is difficult to make the sealing arrangements necessary to get the gases from the ducts on the rotating shell to the outside of the engine.
Various designs of rotary engines and compressors have been disclosed, which have two rotors spinning on offset parallel axes. Examples of these are GB764719, DE2916858, FR1124310 and DE3209807. Taking first GB764719, this design discloses ducts to transfer fluid to and from the working chambers, with the ducts located within a shaft of the machine. However the ducts extend from the working chambers through the rotor, and then into the substantially stationary shaft, which requires a sealing arrangement between these two components. In this arrangement the control of the fluid to and from the working chambers is by means of the rotor rotating about this shaft, meaning that this machine requires seals both to create the working chambers (the spaces between the inner and outer rotors) and seals to control the flow of fluid to/from the working chambers. In addition, the ports and ducts in the inner rotor are bidirectional which can slow the fluid progress, and they are also permanently connected to the working chambers thus increasing the effective chamber volume and reducing the possible compression ration of the machine. The other documents mentioned here, DE2916858, FR1124310 and DE3209807, are all similar with regards to the transfer of fluid to the working chambers.
Cooley proposed an engine (U.S. Pat. No. 724,994) very similar to the invention here, using two axially spinning rotors. In his design the inlet and outlet routes were via sliding seals between the shell and the casing which would make this design problematic and prone to leakage.
Many other rotary engine designs disclose methods of getting the gases into and out of the working chambers, however most have relatively complex ducts containing several moving parts, which causes problems with sealing and heat transfer from hot exhaust gases.
It is the aim of this invention to overcome some of the problems that previously known rotary machines suffer from, that is the difficulty of getting the gases or working fluids into and out of the working chambers from the outside of the machine, the balancing and mechanical problems of eccentric and reciprocating components, seal replacement, insulation of hot gases from component parts and these other designs' general overall complexity.